As it is well known, in the present telecommunications environments, the demand is increasingly pointing toward the provision of greater bandwidth capacity. In the future waves of broadband deployment, service providers are likely to focus on offering a set, as complete as possible, of services in the various domains of voice, data and video to the very household of the end users. These services comprise, for example, video on demand (VoD), HDTV and broadcast TV services for all subscribers simultaneously. In order to achieve this goal broadband access capability is required on the same conventional network implemented for narrowband applications. This means that transmission is made at the broadband and the narrowband rates simultaneously each rate being used for a particular application, e.g. broadband for data communication and narrowband for voice communication.
The simultaneous transmission of broadband and narrowband brings about the need for combining the two types of signal into one in transmission and separating (splitting) the two types of signal into two independent signals at reception.
In the conventional practice, the task of combining and splitting the broadband and the narrowband signals is done by means of the so-called “splitters”. A splitter is therefore a device used in telephony in order to split a telephone signal into two or more signals of different frequencies, or combine signals of different frequencies to form a single combined signal. Splitters are typically installed at central offices and may be needed at customer premises.
One drawback associated with the use of splitters is the wiring work involved in providing a subscriber to a new service is complicated and time consuming. Whenever a new service is activated, for example for providing xDSL service to a user who is already connected to POTS services, the subscriber loop needs to be rewired. This in turn, requires that a technician visits the respective service delivery site, for example a central office or a cabinet, in order to perform the rewiring tasks. The consequence is an increase in costs for providing the new service mainly due to manpower expenses, and perhaps loss of revenue as the service would become available after certain delay, namely only after the completion of the rewiring work.
In order to overcome the above drawbacks solutions have been proposed in order to simplify the use of splitters. One such solution comprises the use of combination line termination cards (hereinafter referred to as “combination cards”). These cards are adapted for combining broadband and narrowband transmissions without using external splitters. These units are single cards that handle both the narrowband access and the broadband access. In order to separate the high rate and the low rate signals from each other, without using an external splitter, combination cards use low pass and high pass filters incorporated inside them.
However, the combination cards also present important drawbacks. These drawbacks can be described within three basic categories:                i—the rigidity of the solution in terms of future evolution;        ii—the upfront investment required for their installation; and        iii—the impact on narrowband service availability caused by a failure in the broadband service.        
These drawbacks are described in further details below:                i—As regards the rigidity of the solution, it is a well known fact in the related art that in a combination card, both the broadband electronics and the narrowband electronics are present in the same physical unit. While narrowband telephony is a very stable technology due to the fact that the existing networks and services need no—or very little—change for their continuing availability, and the operators tend to want to make their investment in such technology last as long as possible (dozens of years or even more); the broadband access technology is changing very rapidly. Furthermore, it is a well known fact that broadband access technology will very probably change significantly every 2-3 years. This strong tendency for change together with the overwhelming demand from the end users for new services, force the operators to replace the already installed plants relatively frequently in their effort to keep up with the fast-changing demand and be compliant with the requirements of the new systems to be installed.        
Therefore, when broadband transmission/reception circuitry is combined in the same physical unit with narrowband transmission/reception circuitry, replacing the broadband part implies also replacing the narrowband part. As a consequence the related narrowband hardware that was intended for lasting many years is discarded, thus giving rise to an unnecessary loss in investment and installation costs.                ii—As regards upfront investment, it is known that the intended advantage of combination card solutions is that the operating expenditures would be reduced when a service is activated to a given user. However, with the integrated combination card solutions the investment already includes both broadband and narrowband hardware technologies from the outset, regardless of whether there would be an eventual need of both services. Thus if the user in question does not demand the combined service, the presence of both types of hardware in the unit gives rise to unnecessary expenditure.        iii—As regards service availability, it is well known that the narrowband telephony is regarded as a high availability service. A level of availability of about 99.999% is a common rate in the related industry. Broadband, on the other hand, has less stringent requirements. If in an integrated combination card the broadband part suffers a failure, the whole card needs to be replaced, thus resulting in the unavailability of the narrowband telephony service as well. The contrary would also be a drawback, namely any failure in the narrowband system, although less probable, would eventually impact the broadband service upon replacement of the single unit combination card.        
In view of the above drawbacks, a solution has been proposed by the applicant as subject-matter of a separate European patent application number 05300911.4 filed on 10 Nov. 2005 according to which two separate line cards, one for narrowband line termination and one for broadband line termination are used, the two line cards being coupled to a common interface device by means of separate connections. The common interface device is adapted for combining the two services, i.e. broadband and narrowband, into one single line, for example one single twisted-pair line from an access multiplexer to a main distribution frame. The common interface device is further designed in a way that allows for independent operation of the two line cards, while at the same time supports the so-called “soft provisioning” concept, namely the ability of switching on and off either one of the above-mentioned services without requiring rewiring work on the subscriber loop. The combination of narrowband and broadband functionalities provides the network operator with ability of activating and deactivating when required, any service on any subscriber line with a simple network management operation.
Moreover, the common interface device comprises auxiliary switching arrangements which can serve as a flexibility point in the system thus allowing the incorporation of additional components or equipment, without major rework on the original system.
A description of said solution is reproduced hereinbelow with reference to FIGS. 1 and 2.
FIG. 1 shows a simplified schematic example of a block diagram of a combined multiservice line termination arrangement 1 according to a first embodiment of the above-mentioned solution contained in European patent application number 05300911.4 for use in an access system. The combined line termination arrangement 1 comprises a first line termination LT1 having a first line card 2 adapted for transmitting and receiving signals in broadband transmission mode, and a second line termination LT2 having a second line card 3 adapted for transmitting and receiving signals in narrowband transmission mode. For example, the first (broadband) line termination LT1 may be adapted for supporting xDSL communication. The corresponding first (broadband) line card 2 may comprise an xDSL baseband circuit for providing connectivity with an xDSL modem as well as a high pass filter 8; and the second (narrowband) line termination LT2 may be adapted for supporting voice telephony, for example a POTS system. The corresponding second (narrowband) line card 3 may comprise a voice codec circuit in order to perform the necessary digital to analog conversion, or vice-versa, in order to adapt the signal for the POTS system, as well as interface circuitry.
The combined line termination arrangement 1 further comprises a common interface device 4 which is coupled, through separate coupling paths, to the first line termination LT1 and second line termination LT2. The common interface device 4 is further connected, through the common port 6 to the main subscriber line 5, for example through intermediate connection from the common interface device 4 to a main distribution frame 7 and from the latter to the main subscriber line 5.
The common interface device 4 comprises a low pass filter 9 and a first switching means 10, such as for example a relay or equivalent, for providing switching combinations as will be described in further detail below.
The low pass filter 9, as its name indicates, is adapted for allowing the passage of relatively low frequencies and for blocking frequencies which are in higher ranges. Typical values for the low frequencies are frequencies below 8 KHz.
Line termination LT1 further comprises a high pass filter 8 in order to block the low frequency signals. Thus the high pass filter 8 may be selected to block frequencies below 8 KHz.
Both filters 8 and 9 are bi-directional, namely they are capable of performing filtering operation in one direction of transmission or the other.
In order to provide additional flexibility points in signal routing, switching means is provided in the common interface device 4. As shown in FIG. 1, a first switching means 10 is placed in an interconnecting position with respect to the common port 6, first line termination LT1 and second line termination LT2, through low pass filter 9.
When the first switching means 10 is placed in position A, the common port 6 is directly connected to the first line termination LT1 through the coupling path A1 and is further connected by means of the coupling path A2 to the second line termination LT2 through the low pass filter 9.
In transmission, line termination 1, having the line card 2 transmits broadband signals to the common interface device 4 through the high pass filter 8. As the broadband signals are of high frequencies, the high pass filter allows a substantially complete passage of the signal through, which is then output from the common port 6. Low pass filter 9 blocks the passage of the broadband signal towards the line termination LT2.
On the other hand, the line termination LT2 transmits narrowband signals to the common interface device 4. These signals pass through the low pass filter 9 which allows a substantially complete passage of the narrowband signal which is then output at the common port 6. High pass filter 8 blocks the passage of the narrowband signal towards the line termination LT1.
In reception, a combined narrowband and broadband signal input at common port 6 in directed, through the coupling path A1, towards the first lines termination LT1 where the low frequency part of the combined signal is blocked at the high pass filter 8 and the high frequency signal is allowed to pass towards the broadband line card 2. The combined signal input at common port 6 also is fed, through the coupling path A2, to the low pass filter 9 which blocks the high frequency signals and allows the passage of the low frequency signals towards the second line termination LT2 and thus towards the narrowband line card 3.
Therefore in this arrangement both the broadband and narrowband transmission and receptions modes are available.
However, situations may arise where the broadband service provided by the first line termination LT1 needs to be interrupted, for example because the existing broadband service needs to be replaced by a service based on a newly developed broadband technology; or where there is a need to provide connectivity with an external broadband equipment to the subscriber line, while maintaining unchanged the narrowband service provision from the line termination LT2.
In such cases, the switching means 10 may be placed in position B, where the first line card LT1 is disconnected from the common port 6 and the common interface device 4 only operates with narrowband services through the coupling path B1. In this arrangement also, the low pass filter 9 serves for blocking any incoming high frequency signal while the broadband service is delivered or received from an external system (not shown).
FIG. 2 shows a further embodiment of the solution proposed in the above-mentioned European patent application number 05300911.4 wherein a second switching means 11 is used. In this figure, features similar to those of FIG. 1 are given the same reference numerals.
An example of a situation where a second switching means may be necessary is where there is a need to provide a smooth migration from old equipment (e.g. local exchanges) to the new equipment. In such a case, it may be assumed that the old local exchange subscriber line is connected to connection port 12 of the common interface device 4 through connection point C of the second switching means 11. Broadband service from the first line termination LT1 is activated or deactivated, based on the specific requirements of each application, by changing the position of switching means 10 as previously described in relation to FIG. 1.
Therefore, in case it is desired to perform a full migration operation from an old local exchange to a new equipment, for example in order to decommission the old local exchange, the operation can be performed by a simple change in the position of the second switching means 11 from position C to position D without a need to visit the respective site. In position D, connectivity is provided through connection port 13 towards the newly connected line termination LT2 provides narrowband service using the narrowband line card 3 as previously described in relation to FIG. 1.
While the subject-matter of the European patent application number 05300911.4 provides a solution for combining signals of different type for transmission and separating signals of different type combined in one into separate signals by using separate line cards that operate independently from each other, circumstances may occur where it may become necessary to provision arrangements for switching in or switching out equipment from the system according to specific requirements not mentioned detail in said European patent application. The equipment to be switched in or switched out may be related to broadband or narrowband services as the specific conditions of each case may require.
The present invention provides solution for such specific requirements as will be described in more detail below.